Chemical vapor deposition (CVD) and atomic layer deposition (ALD) have been adopted as the main deposition technique for depositing thin films to comply with the scaling down of semiconductor devices because CVD and ALD enables achievement of films (metal, oxide, nitride . . . etc) of finely defined thickness and high surface/step coverage. The film growth results from the chemical reaction of organometallic compounds (precursors), so it is essential to develop optimum precursors and understand its reaction process.
Precursors have been developed to attain required properties based on its application to certain types of desired film. However several basic properties should be considered to achieve good quality films. First, sufficient vapor pressure is necessary for easy delivery into the reaction chamber from containing vessel. Second, excellent thermal stability is required during the storage in the vessel at the storage temperature before delivery. Third, strong reactivity toward reacting gas is required to be readily converted into desired film in the deposition chamber. Another important requirement is controlling impurities in the film, which is usually originated from the ligand during the deposition process, has to be considered at the stage of precursor design.
Some group IV metal precursors have already been developed and used to deposit oxide or nitride metal films. The main titanium precursor is tetrachloro titanium, TiCl4. It is widely used to make titanium-containing films. The use of molecules such as tetrakis(dimethylamino) titanium (TDMAT) and tetrakis (diethylamino) titanium (TDEAT) for titanium oxide in ALD mode with H2O have already been reported. See, e.g., EP0503001. Some nitride films were also deposited using ammonia as a co-reactant.
In the case of zirconium, tetrakis(dimethylamino) zirconium (TDMAZ) is now a standard material used to deposit zirconium-containing films, especially zirconium oxide. The low decomposition temperature of the molecule remains a problem in many processes.
Besides the above mentioned precursors, new molecules have also been developed.
Patent application publications (see, e.g., US 2008/0102205 and KR 2007/0121281) mention the use of cyclopentadienyl containing compounds, such as those shown below, as CVD/ALD precursors.
Biscyclopentadienyl triisopropyl-guanidinato titanium(III)                wherein A=NR2R3 or ER4,        E=O or S, R1═H, Me, or Et,        R2 & R3═C1-C4 alkyl w/opt        F group or SiR53,R4═C1-C6 alkyl w/opt F group or SiR53 & R5═C1-C4 alkyl.        
Molecules having two or three alkylamino ligands, together with ethylenediamino ligand, aminoalkylamino ligand, and guamidinato ligand have been mentioned as CVD/ALD precursors of Group IV metal nitride, metal oxide, and metal electrode applications (see, e.g., US Pat App Pub No 2009/0036697 and WO 2009/012341).
                wherein R1, R4═C1-C6 alkyl,        R2, R3═H or C1-C3 alkyl, & R5,        R6═C1-C4 alkyl        wherein R1-R10═H, C1-C12         alkyl, C1-C12 alkylamino, C1-C12         alkoxy, cycloalkyl, C2-C12         alkenyl, C7-C12aralkyl, C7-C12         alkylaryl, C6-C12 aryl, C5-C12         heteroaryl, perfluoroalkyl,        & Si-containing groups        
Some patent application publications mentioning the use of imido type compounds with a Group IV or V metal, shown below, as catalysts for polymerization are also available (see, e.g., WO 2005/123790 and WO 2008/148499).
                wherein R—R9═C1-C20 alkyl        or aryl group, La=coord ligand,        & X1=anionic ligand        wherein N═Y is anionic imine        ligand, X=hydride or hydrocarbyl        
On the synthesis side, many research articles regarding chemistry of cyclopentadienyl imido titanium have been published by the Philip Mountford group at University of Oxford: Dunn et al., J. Chem. Soc., Dalton Trans., (1997), 293-304; Stewart et al., J. Organometallic Chemistry 564 (1998) 209-214; Stewart et al., Organometallics 17 (1998) 3271-3281; Guiducci et al., Organometallics 25, (2006), 1167-1187. Some of the molecules described are shown below.
Among the developed molecules, some were liquids, but their thermal stability was not indicated. Applicants believe that such molecules were never considered for semi-conductor applications.
Some research articles about CVD/ALD using imido type metal precursors, some shown below, have been published by the C. J. Carmalt group at University College London: C. J. Carmalt et al., “Synthesis of TiN thin films from titanium imido complexes”, Journal of Materials Chemistry 13, 2003, 84-87; C. J. Carmalt et al., “Titanium imido complexes as precursors to titanium nitride”, J. Chem. Soc., Dalton Trans., 2002, 4055-4059; Potts et al., “Tungsten Imido Complexes as Precursors to Tungsten Carbonitride thin films”, Dalton Transactions 2008, 5730-5736.

The widespread use of TiCl4 results in the introduction of chlorinated by-products in the deposition line. These chlorinated by-products are undesirable due to their corrosiveness and toxicity. Other molecules currently in use, such as TDMAT and TDEAT, exhibit poor thermal stability, making it impossible to use them for high-temperature (up to 400° C.) depositions, particularly in ALD model.
The need remains for the development of halogen-free molecules that enable deposition of films with controlled thickness and composition at high temperatures.